Cambodian opposition leader Sam Rainsy said his country has reached a political "stalemate" and is calling for a halt in international aid to the Phnom Penh government.

Rainsy spoke to VOA during a visit to Washington, where he is trying to convince U.S. officials and others to put more pressure on Prime Minister Hun Sen to allow an independent probe into a contested July vote.

Although official results show Rainsy's Cambodia National Rescue Party made substantial gains in the election, opposition lawmakers have refused to take their seats and claimed the long-time ruling party committed voter fraud.

Following meetings with U.S. Deputy Secretary of State William Burns, Rainsy told VOA many in Washington remain sympathetic to his position.

"Officials in the U.S. that I have met understand the situation in Cambodia very well. They understand the recent elections were problematic and that the results as proclaimed by the authorities are controversial," said Rainsy.

Rainsy also met with officials from the World Bank and the International Monetary Fund but did not say whether he has had any success in convincing officials to change their behavior toward the Cambodian government, which is heavily dependent on foreign aid.

State Department spokeswoman Jen Psaki said this week that Rainsy's meetings with U.S. officials did "not signify an endorsement." She insisted the U.S. supports an "open and democratic process" in Cambodia rather than a single party.

However, Psaki also renewed the U.S. State Department's call for a "credible and transparent review" of the election.

"Independent observers have noted serious election irregularities. We do believe and continue to believe that a credible and transparent review of the election would help efforts moving forward," said Psaki.

Rainsy's party has already held a series of large protests and is threatening more demonstrations for next week. He is also considering a general strike to put more pressure on the government.

The 64-year-old, who was barred from running in the election, claims his party will not back down on its parliamentary boycott. He also said that several rounds of talks between himself and Prime Minister Hun Sen have gone nowhere.

"There is a stalemate. A real deadlock. Because we insist on a real investigation into election irregularities, whereas Prime Minister Hun Sen wants to move forward regardless of the truth regarding the result of the elections," declared Rainsy.

"The constitution states that Cambodia should follow a democratic system based on pluralism, but actually Cambodia has returned to a one-party system. So this is a clear violation of the constitution that makes the current Cambodia [government] illegal, or at least illegitimate," Rainsy continued.

Prime Minister Hun Sen, who has ruled the country since 1985, has said the vote was fair and argues that the results were upheld by Cambodia's National Election Commission and Constitutional Court.